I have a paid account that has never been used to store data. Your faq for cancelling states;

"If you are a Paid Account, first open the subscription history page, by clicking on "My account -> Subscription/unsubscription". Click on Cancel Subscription, the operate will discontinue your service immediately. Refunds are not offered for the unused portion of your service period, so we always suggest you cancel at the end of the current period, which you have already paid for. "